[jdk16] RFR: 8260585: AArch64: Wrong code generated for shifting right and accumulating four unsigned short integers

[Dong Bo]

This is a typo introduced by JDK-8255949.
Compiler will generate `ushr` for shifting right and accumulating four short integers.
It produces wrong results for specific case. The instruction should be `usra`.

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Commit messages:
 - 8260585: AArch64: Wrong code generated by shifting right and accumulating four unsigned short integers

Changes: https://git.openjdk.java.net/jdk16/pull/136/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk16&pr=136&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260585
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk16/pull/136.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16 pull/136/head:pull/136

PR: https://git.openjdk.java.net/jdk16/pull/136